1. Field of the Invention
The present invention relates to the tempering of glass sheets. It has always been a problem in tempering glass sheets to provide apparatus that is readily adjustable for handling glass sheets of different curved configurations. Prior to the present invention, it was very difficult to adjust tempering apparatus to adapt the apparatus for widely different sizes and configurations of different production patterns. Alternatively, different apparatus was required for widely different patterns, particularly those patterns in which the end portions of the glass sheet were bent about axes of bending into planes oblique to both the length and width of the flat development of the bent glass sheet. Also, it has been difficult to adjust prior art tempering apparatus to conform to flat as well as curved shapes.
2. Statement of Technical Problems and Description of Patents of Interest
The process of tempering glass sheets is well known. Conventionally, a glass sheet is tempered by a two step process in which the glass is first heated to an elevated temperature sufficiently high for tempering followed by very rapid cooling to a temperature below the strain point. When glass is tempered, the glass sheets so treated develop a stress pattern in which the tempered glass develops a thin skin of compression stress surrounding an interior stressed in tension. Such a stress distribution through the thickness of the glass makes the glass sheet much stronger then untempered glass so that tempered glass is less likely to fracture than untempered glass when struck by an object. Furthermore, in the less frequent times when an outside force is sufficiently large to cause tempered glass to fracture, tempered glass breaks up into a large number of smoothly surfaced, relatively small particles, which are far less dangerous than the larger pieces with jagged edges that result from the more easily induced fracture of untempered glass.
Typical prior tempering apparatus includes sets of nozzles extending from plenum chambers or nozzle boxes to direct a plurality of cold air blasts against the opposite major surfaces of a glass sheet in directions approximately normal to the opposite localized portions of the major surfaces. Unless there is relative motion between the glass sheet and the nozzles, irisdescent patterns form on the surface of the tempered glass. These patterns of irisdecence develop because fixed air blasts cool fixed locations opposite the blasts rapidly while other locations on the glass sheet intermediate the impingement of air blasts are not cooled as rapidly. When the distance from nozzle to glass differs too greatly between adjacent nozzles, non-uniform cooling of adjacent glass portions may result, also leading to irisdescence.
The glass sheet tempering art has developed many techniques for imparting relative motion between the arrays of nozzles that face the opposite surfaces of a glass sheet to avoid irisdescent patterns. Some of these involve linear reciprocation of the nozzles. Others involve linear movement of glass sheets or linear reciprocation of glass sheets past an array of fixed opposing nozzles. Others involve applying orbital movement (elliptical or circular) of nozzles relative to a glass sheet supported at a fixed position.
The shape of the glass to be tempered and its manner of support between plenum chambers determines the best technique for providing relative movement between the nozzle arrays extending from the plenum chambers and the glass sheet to be tempered. When glass sheets are bent about one sharp axis of curvature, the glass sheet or the nozzle arrays are preferably linearly reciprocated along lines substantially parallel to the sharp axis of curvature. When the glass sheets are shaped and then supported in an essentially horizontal configuration for movement through a cooling station on a ring-like outline supporting member, the glass sheet is supported between upper and lower sets of nozzles whose discharge ends are arranged in surfaces approximately parallel to the curved shape of the glass sheet. Thus, the nozzle to glass distance remains substantially constant during the application of cool tempering medium while providing relative motion. In order to avoid the wear and tear on the flexible air supply elements for tempering apparatus and to avoid the need for large energy consumption in the movement of the tempering apparatus relative to the glass, it has been found preferable to linearly reciprocate the ring-like member which supports the shaped glass sheet between sets of upper and lower nozzles which apply blasts of cold tempering medium, usually air, against the upper and lower major surfaces of the shaped glass sheets supported on the outline ring-like member.
When glass sheets are shaped to complicated shapes having sharp lines of bending that extend oblique to the direction of reciprocation, in order to avoid collision with one or more nozzles, it is necessary that the nozzles be separated by a sufficient vertical distance to permit the shaped glass sheet to move into and out of a position between the nozzles at the shaping station. The nozzle sets need not be so widely separated to allow the glass sheet to be reciprocated a sufficient distance to avoid collisions with nozzles if the nozzle ends are arranged parallel to the glass shape within the area of glass sheet reciprocation. It is also necessary that the nozzle ends be a sufficiently short distance from the opposite major surfaces of the glass sheet during the application of the cold tempering medium so that the blasts of tempering medium applied to the glass be capable of rapidly cooling the glass surfaces. This cooling action is a function of the speed of movement of the blasts against the glass surfaces. However, when the nozzle to glass distance is too short, the hot glass surfaces are likely to distort on initial impingement.
When glass sheets are shaped by the bending method depicted in U.S. Pat. No. 3,846,104 to Samuel L. Seymour, wherein a horizontally oriented glass sheet is heated and lifted by a lower bending mold into contact with an upper bending mold where it is retained by vacuum until the lower bending mold retracts to allow a ring-like member to receive the bent glass sheet and convey it from the bending station into a tempering station, the ring-like member supports the bent glass sheet in a substantially horizontal orientation. The bent glass sheet is reciprocated while mounted between the nozzle arrays on the ring-like member in a direction parallel to the path of movement of the glass from the shaping station to the cooling station. If the axis of the sharp glass sheet bend deviates considerably from an axis parallel to the axis of reciprocation, the tempering nozzles interfere with the glass sheet reciprocation unless the arrays of nozzles are separated from the bent glass sheet by sufficient distance and the reciprocation displacement is sufficiently small to provide clearance for reciprocating the bent glass sheets between the nozzles. If the arrays of nozzles beyond the axes of sharp bending are not capable of adjustment in response to changes in size of the pattern and to changes in the orientation of the lines of sharp curvature, an arrangement of nozzle arrays suitable for cooling sheets of one shape would be totally unsuitable for cooling sheets of a different shape. The same problem exists when a change of size is involved from pattern to pattern. Either certain nozzles would be too far from certain regions of the bent glass or too close or even touching other regions of the bent glass during reciprocation of glass pattern relative to nozzles arranged for a shape or size different from a previous pattern.
Prior to the present invention, the modifications available for rearranging sets of tempering nozzles were limited to conforming to shapes other than those incorporating sharp bends about oblique axes if the nozzle ends were close to the glass. In order to avoid collisions with nozzles during reciprocation, the nozzles had to be arranged at greater distance from the glass. Since the force of nozzle blasts lessens with travel distance to the glass surface, more energy was needed to provide cold air blasts with greater force to assure adequate surface cooling to develop an adequate temper.
U.S. Pat. No. 2,677,918 to Bird et al. discloses apparatus for tempering curved glass sheets having nozzles that are adjustable in length to locate the ends of the nozzles in curved surfaces substantially parallel to the shape of the major surfaces of a bent glass sheet undergoing cooling. Generally, the nozzle arrays are adjustable for bends of non-uniform radii of bending about substantially parallel axes.
U.S. Pat. No. 2,790,270 to Freiberg discloses apparatus for tempering horizontally supported glass sheets that are sharply curved at their longitudinal ends. This patent has a pair of pivoting wing boxes flanking main nozzle boxes and incorporates means for adjusting the manner in which the wing boxes are constrained to pivot about horizontal axes with respect to the main nozzle boxes. The pivoting wing boxes follow different curved shapes about transverse horizontal axes of elongated sharply bent glass sheets. This patent also adjusts the length of the apparatus to receive sheets having different lengths between the axes of sharp bending.
U.S. Pat. Nos. 2,876,592 and 3,008,272 to Black et al. use track sections that are linked together to provide curved paths for engaging the ends of nozzle boxes that move in unison in curved paths parallel to the opposite surfaces of bent glass sheets. This apparatus is limited to treating glass sheets whose curvature is substantially of the same radius from one transverse side edge to the other transverse side edge although the radius may vary along the longitudinal dimension of the glass.
U.S. Pat. No. 3,024,572 to Richardson discloses apparatus for tempering curved glass sheets in which a plurality of rows of nozzles are each individually adjusted toward and away from the position occupied by the major surfaces of the glass sheet so as to have the ends of the nozzle rows lie in curved planes parallel to the curvature of the glass sheet and to one another.
U.S. Pat. No. 3,294,518 to Laseck et al. discloses apparatus for tempering curved glass sheets of different lengths but substantially uniformly curved ends. A plurality of slot nozzles is provided with means for moving the nozzles lengthwise of the slots. Adjacent alternate slots overlap one another at their ends so as to accommodate longer and shorter glass sheets having substantially uniform curved ends in the space between the opposite sets of slotted nozzles.
U.S. Pat. No. 3,799,752 to Cheron discloses tempering nozzles that are articulated so as to assume transverse curvatures that conform generally to the shape of glass sheets being chilled. The cross-sectional shape is uniform along the length of the cooling apparatus.
U.S. Pat. No. 4,071,346 to Schmidt discloses a plurality of axially adjustable nozzles in apparatus for tempering curved glass sheets with inflatable means to lock the nozzles in different positions so as to have the nozzle ends conform to the surfaces of the glass sheets undergoing cooling.
U.S. Pat. Nos. 4,140,511; 4,142,882; and 4,157,910 to Imler disclose nozzles that attach in pivotal relation to nozzle support elements that are movable relative to the glass thickness. When the support elements pivot, blasts from the nozzles sweep across localized sections of a glass sheet of flat or curved configuration undergoing cooling. This apparatus does not need movement either of the glass sheet or the entire tempering apparatus.
U.S. Pat. No. 4,343,645 to Abe discloses apparatus for tempering curved glass sheets. The apparatus includes end nozzle boxes that are adjustable in shape by virtue of adjustable side walls. This apparatus also includes replaceable nozzles to adapt the apparatus for either full temper or partial temper.
None of the patents provides tempering apparatus for horizontally supported bent glass sheets comprising end nozzle boxes capable of pivoting about vertical axes to positions obliquely disposed with respect to centrally disposed nozzle boxes and linearly adjustable relative to the centrally disposed nozzle boxes so as to enable glass sheets bent about axes oblique to their length to reciprocate between upper and lower sets of nozzles having their ends arranged along curved surfaces conforming to the longitudinal curvature of the glass sheets undergoing tempering. None of these patents disclose glass sheet tempering apparatus having end nozzle boxes adjustable in position to have apertured walls extend in planes that are approximately parallel to obliquely extending end portions of the bent glass sheet that are bent about oblique axes relative to the length and width of the flat development of the bent glass sheet.
None of the patents provides tempering apparatus having centrally disposed open-ended nozzle boxes provided with readily removable nozzles to permit end plenums to move slidably relative to the ends of the nozzle boxes to conform to different lengths of the central portion of different glass sheet patterns. None of the patents provides pivotable adjustment of end nozzle boxes to provide a straight as well as a curved space to receive flat glass sheets as well as sharply bent glass sheets for tempering.